Patient positioning in clinical work has been found the most difficult subdomain in dental narrow-beam tomography. When considering the actual imaging occasion, thus ignoring the development of film, an incorrect patient positioning is the most common reason for having to do a retake and thus for unnecessary increase of a radiation dose that a patient is exposed to. Approximately, as much as up to 20% of images must be retaken as a result of incorrect patient positioning. Thus, all efforts intended for securing a patient position and simplification of patient positioning will be to the benefit of a patient in the form of a decreased radiation dose.
Patient positioning and determination of the position of a patient are significantly based on the evaluation of the position and location of the head, neck and shoulders of a patient. In the patient positioning involved in dental imaging, a primary objective is the positioning of a patient in the imaging apparatus symmetrically in a manner that, on one hand, the front and molar teeth and, on the other hand, both upper jaw and lower jaw teeth can be positioned at the sharply imaged layer. Furthermore, the plane of occlusion is set horizontal, the neck column is straightened, the patient is positioned to lean slightly backward and his or her shoulders are pressed as low as possible. It is necessary to make compromises between various objectives with patients in general and especially with asymmetric patients.
The general instruments in patient positioning include an occlusion brace for setting the upper and lower jaw teeth in the same plane, a chin brace, a forehead brace, temple braces, handgrip means as well as various light lines focused on the face of a patient. However, no final solution to the problems of patient positioning has been found and no support systems or light lines can make sure of a successful patient positioning without the judgement and consideration of an operator. The reliability of judgement is substantially improved if positioning is easy to perform and the operator is able to see the face of a patient as clearly as possible. Essential in the judgement of symmetry is that the operator sees the patient directly from the front.
The instruments are intended for the use of a dentist employee in either the standing or sitting patient position. In general, an apparatus designed for a standing patient can also be used for a sitting patient position by fitting it with a regular chair. The equipment intended for hospital use can also employ a lying patient position. In the prior art equipment employing a standing patient position, the patient is directly facing the support column of said apparatus, i.e. the component that carries imaging equipment and patient positioning instruments. For reasons of saving space, the support column is usually set by a wall so the patient, almost without exception, is also facing the wall. Nearly all such instruments are provided with a mirror for the operator to see the face of a patient. Through an inclined mirror, however, it is impossible to obtain a symmetric viewing angle to the face of a patient. Due to mutual differences in the heights of an operator and patient, all the operator often can see in the mirror is just the forehead or arm of a patient instead of his or her whole face.
In the above-described equipment it is generally possible to use a patient chair and, thus, a sitting patient positioning. However, the knees of a grown-up patient will then without exception hit the column and, as positioned to flank said column, the knees will be in the way of an operator. The same applies also to the equipment totally based on a sitting patient position and in which a patient is facing the column. In such equipment, the plane of examination of an operator lies considerably higher than the face of a patient and, thus, all that is visible in the mirror are the arms of a patient.
In the prior art equipment employing a sitting patient position and in which a patient is facing away from the column and wall, the above problems of seeing a patient do not occur. However, the patient support equipment, chin and temple braces, must be turned aside when a patient is placed in the device and correspondingly when he or she is leaving the device. These devices are not fitted with a forehead brace either, which is one of the most critical components for reliable patient positioning. Furthermore, in these devices, the X-ray tube passes between the column and patient which is why the patient must be brought further away from the column. As a result, such equipment requires more space.